Field of the Invention
The present invention relates to an object information acquiring apparatus.
Description of the Related Art
Conventionally, an object information acquiring apparatus, such as a photoacoustic imaging apparatus and ultrasound echo imaging apparatus, has been proposed as technology for acquiring information on the interior of an object, such as a living body, by receiving acoustic waves. Photoacoustic imaging apparatuses are used widely, particularly in the diagnosis of skin cancer and breast cancer, and are expected to replace conventionally used devices, such as ultrasound echo diagnostic apparatuses, X-ray apparatuses, MRI apparatuses, and so on.
When a living body tissue is irradiated with measurement light, such as visible light or near-infrared light, the light absorbing material in the living body, for example, material such as hemoglobin in blood, absorbs the energy of the measurement light and momentarily swells, giving rise to an acoustic wave. This phenomenon is called the photoacoustic effect, and the acoustic wave generated thereby is called a photoacoustic wave. Photoacoustic imaging (PAI) is a technology which makes information about living body tissue visible by measuring this photoacoustic wave. A technique of cross-sectional imaging using photoacoustic waves is called “photoacoustic tomography (PAT)”.
In photoacoustic imaging, information relating to the absorption coefficient of the interior of an object can be converted into an image. The absorption coefficient is the ratio at which the living body tissue absorbs light energy. The information related to the absorption coefficient is, for example, the initial sound pressure, which is the sound pressure at the moment that the photoacoustic wave is generated. The initial sound pressure is directly proportional to the product of the light energy (light intensity) and absorption coefficient. Consequently, it is possible to acquire the absorption coefficient by carrying out suitable processing on the value of the initial sound pressure.
Moreover, the absorption coefficient is dependent on the concentration of the components which constitute the living body tissue. Therefore, it is possible to acquire the concentration of the constituent components from the absorption coefficient. In particular, it is possible to acquire the density ratio of oxygenated hemoglobin and reduced hemoglobin and the oxygen saturation of the living body tissue, by using light of a wavelength that can be absorbed readily by hemoglobin in the blood. By analyzing the oxygen saturation distribution, application to medical diagnosis, such as determination of tumor tissue and peripheral tissue inside the living body, is expected.
“Minghua Xu and Lihong V. Wang, “Analytic explanation of spatial resolution related to bandwidth and detector aperture size in thermoacoustic or photoacoustic reconstruction”, PHYSICAL REVIEW E 67, 056605 (2003)” discloses an ultrasound wave probe having a round cylindrical surface shape. Furthermore, the resolution of the photoacoustic imaging is indicated for respective probe shapes, such as a flat surface, cylindrical surface and spherical surface. Moreover, it has been disclosed that a high-resolution region is located near the center of curvature of a spherical surface-shaped probe.
Non Patent Literature 1: Minghua Xu and Lihong V. Wang, “Analytic explanation of spatial resolution related to bandwidth and detector aperture size in thermoacoustic or photoacoustic reconstruction”, PHYSICAL REVIEW E 67, 056605 (2003)